Method and apparatus for the transmission of signals



Jan. 21, 1947. v

H. DE FRANCE METHOD AND APPARATUS FOR THE TRANSMISSION OF SIGNALS FiledAug. 24, 1942 0 c; Q o o G 0 O S uvvewroz? Patented Jan. 21, 1947 METHODAND APPARATUS FOR THE TRANSMISSION OF SIGNALS Henri de France, Lyon,France; vested in the Alien Property Custodian Application August 24,1942, Serial No. 455,909 In France January 26, 1942 4 Claims.

The present invention relates to methods and apparatus for thetransmission of signals to a distance of the kind including, both fortransmission and for reception of said signals, electronic means towhich energy is fed from suitable feed sources, for instance from acyclical or alternating current distribution system. The invention ismore especially, although not exclusively, concerned with these methodsand apparatus as applied to television and especially television systemsincluding mobile transmitting (and even receiving) stations.

The object of the present invention is to provide a method and apparatusof the type above referred to which ensures a more accurate receptionthan was possible up to the present time, this result being obtained, inparticular, Owing to the elimination of the defects which are due, inthe present practice, to the lack of synchronization between the feed atthe transmitting station and the feed at the receiving stations.

With this object in view, an essential feature of my method consists inindependently feeding alternating current to one of the stations andespecially the transmitting station and synchronizing this feed to astandard frequency which may be supplied for instance by an alternatingcurrent distribution system. The synchronizing may be eiiected eitherthrough a cable or through radio electric means, this last methodensuring a great freedom of the independently fed station which can thusbe a mobile station.

According to an essential feature of my invention, my apparatus includesan independent source of alternating current at one of the stationsbetween which signals are to be transmitted and more especially at thetransmitting station, a central source of standard frequency and meansfor synchronizing this independent feed source with said central source.

According to a preferred embodiment and especially when a plurality ofreceiving stations are to receive signals from a transmitting station,the central source of standard frequency and the receiving stations areall fed with alternating current by a common distribution system.

Other features of the present invention will result from the followingdetailed description of some specific embodiments thereof.

Preferred embodiments of the present invention will be hereinafterdescribed with reference to the accompanying drawing, given merely by'way of example and in which:

Fig. 1 is a diagrammatical view of a system according to the presentinvention and especially intended for television, such a systemincluding a fixed central transmitter, a plurality of receiving stations(one of which is shown at I 8 on the drawing) and a mobile transmittingstation the signals of which are intended to be received by the centraltransmitter so as to be retransmitted.

Fig, 2 shows a portion of a system of the kind of that shown by Fig. 1,this portion being that relating to the feed of the transmittingstation, this embodiment corresponding to a modification of that shownby Fig. 1.

In the following description, it will be supposed that the invention isapplied to the case of a television system including a mobiletransmitting stationthat is to say a transmitting station carried by avehicle.

First, it must be remembered that in the systems of this kind such ashave been made up to the present time, the mobile transmitting stationis fed with current from an external source, generally a 50 cyclealternating or reciprocating current distribution system, which may bethe same as that used for the feed of the various fixed (or mobile)receiving stations, or which may be distinct.

Such systems have the disadvantage that the field of possibleapplications is considerably reduced. As a matter of fact, it may benecessary to perform television transmission at places where the powerof the current that is available from the distribution system isinsufiicient, or again at places where no plug-switch has been provided.On the other hand, television transmission can take place only when thevehicle is stationary. It is impossible when the vehicle is moving.Furthermore, it has been found that when the feed is ensured byalternating current (or by direct current obtained by rectification ofalternating current) both at the transmitting station and at thereceiving stations, it is necessary to ensure that the frequencies ofthe feed sources, at transmission and at reception, be perfectlyidentical and synchronized. This is necessary because if there is aphase difference between the tube heating current at the transmissionstation and the tube heatin current at the private receiving stations,there results, on the screens of said receiving stations, a successionof moving bands alternately dark and clear and also a certain stirringin the direction of the lines, this result being due to the combinedeffect of the lack of synchronism and of the defects of the filteringmeans in the feed circuits.

The object of the present invention is to eliminate these drawbacks and,in particular, to permit, with a transmitting station carried by avehicle, of performing television under any conditions whatever, evenwhen the vehicle is moving, while avoiding at the reception the defectsdue to lack of synchronism between the feed sources.

For this purpose, according to the invention, I proceed in such mannerthat:

(a) The mobile station (to wit, in the particular case that is beingconsidered, the transmitting station although the invention might aswell apply to the feed of mobile receiving stations) includes,independent alternating current feed means of any suitable type; and

(b) This alternating current (for instance of the 50 cycle type) issynchronized, through any suitable means, to a standard frequency whichwill preferably be that of a current distribution system.

If it is supposed, as it will be the case in the following description,that the receiving stations are fixed stations in which the heating isitself ensured through said distribution systems, a perfect synchronismwill thus be always obtained.

Furthermore, it is advantageous, according to another feature of myinvention, to ensure synchronism to a distance through radio-electricsignals, whereby the vehicle which carries the transmitting station,with its independent current feed, can freely perform any desireddisplacement.

A system complying with the conditions above set forth can be made inmany difierent ways,

for instanc as follows:

Concerning first the mobile transmitting station carried for instance bya trailer 2 attached to a vehicle I, its general arrangement is of anysuitable type. For instance it includes a camera apparatus 3, thevarious usual television devices (supposed to be carried by the vehicleproper, l) and an antenna 4.

As for th means for feeding current to said transmitting station, theyare advantageously carried by a trailer 2. They include a suitablesource of energy, for instance an internal combustion engine 5 (or anymotor operated by a .fluid) or an electric battery. This source ofenergy is capable of driving or controlling an apparatus for generatingalternating. current, which apparatus may for instance be either of thelectro-dynamic kind, being then advantageously constituted by analternator 6 (Fig. l) or of the electrostatic or other kind as shown byFig. 2. In the embodiment of Fig. 2, said apparatus is constituted by agroup of gas tubes or thyratrons l, assembled in any known manner fortransforming a direct current (fed for instance by a battery or, asshown by the drawing,,by a generator 8 driven by the internal combustionengine 5.) intoan alternatingicurrent Concerning finally the means forsynchronizing the frequency of this alternatingcurrentfwith that of thedistribution system that is chosen, said means are made in such mannerthat, through an alternating current fed to a distance,

transmittedthrough radio-electric means, then received by a suitablereceiving device 9, provided at the mobile television transmittingstation, it is possible to influence one'of the factors upon whichthefrequency of this current depends in the alternatingcurrentgenerating system of said station.

Thus I may make use of a transmitterii] of relatively low power,'locatedat any suitable place (for instance at the central transmission stationabove mentioned). This transmitter is modulated by means of thefrequency of the current distribution system, which gives for instance aWave modulated to 50 cycles. Then this wave is received in receiver 9,which is fitted with demodulating means of any suitable type. At theoutput end of this receiver, I thus obtain an alternating current whichis in accurate synchronism with the current distribution system. I maythen utilize this current in one of the following ways:

(a) Thi current is caused to act upon a device analogous to aphase-meter which is otherwise influenced by the frequency of thecurrent fed by the source of the mobile station, for instance alternator6, this device producing a voltage or a current which is a function ofthe phase difierence and through which it is possible to control all theelements or circuits upon which the frequency'of said station depends;

(b) The current from device 5 may also be caused to act directly uponthe source of alternating current of the mobile station and especiallywhen the latter is constituted by thyratrons. It is known that thedischarge of such tubes can be controlled by a suitable alternatingcurrent, and at the frequency of said current;

(0) Other possible ways of utilizing the current from device 9 areincluded in my invention.

In Fig. 1, I have showmby wayoi example, a phase-meter li receiving, ontheone hand, the

sinusoidal current from receiver 9 and, on the other hand, a currentfrom alternator 6 which is intended to feed the elements of thetransmitter [Z of the vehicle. The variable current resulting from theaction of the two above mentioned currents may be used for operating anymechanical, electronic, or other relay capable of modifying the speed ofrevolution of the alternator.

I might, for instance, act, through such a relay, either upon the fuelfeed means of engine 5, or on any electrical intermediate deviceinfluencing the control of the operation of the alternator.

It has been supposed, in the example shown by Figure 1, that theinternal combustion engine 5 drives alternator 6 through theintermediate of a generator l3, the current of which is fed to anelectrical motor l coupled with the alternator. The current fed by thephase-meter then comes to act, either through rheostat 53 or throughelectronic relays, or again through other means, upon the excitationmeans of the generator or motor. But this arrangement is given merely byway of example and has no limitative character. In particular, I mightutilize the means described in the French Patent No. 869,107 filedby'Mr. Yves Rocard, on September 13, 1940, and concerning the controland the adjustment of electrical motors, the means described withreference to Fig. 2 of said French patent being particularly suitablefor this purpose. 4

In Fig. 2, I have shown an arrangement including 'thyratrons l. Thelatter are fed with the direct current supplied by generator 8 coupledwith motor 5. On the other hand, they are controlled, in the knownmanner, by the sinusoidal current supplied from receiver 9. Thealternating voltage at the output of the-thyratrons is then exactly at the samefrequency as that receive in said receiver.

Whatever be the particular embodiment that is chosen within the scope ofmy invention, I obtaina system theworking of which is such that the feedof the mobile transmitting station will be always synchronized with thatof the receiving stations which are supposed to be connected to theelectric distribution system. It should be well understood that thismobile transmitting station may either transmit the signals directly ifits power is suliiciently great, or transmit signals intended to bereceived by a powerful central transmitting station which retransmitssaid signals, such a central transmit-er being shown at I! in Fig. 1.

The synchronizing transmitter l0 may be adjoined to this centralstation. In all cases, the construction according to my inventionpermits of fully solving the problem of mobile television stations. Itensures a perfect synchronizing between the feed of the transmitter andthat of the receivers, while leaving the vehicle which carries thetransmitter entirely free to move during the television process.However, when television has been performed at a fixed place, it is ofcourse possible to obtain the desired synchronization by connecting thephase-meter or any other adjustment apparatus with the local electricdistribution system through a cable.

Finally, there is always a suitable power available, to wit thatprovided for the source of energy mounted on the vehicle.

In a general manner, while I have in the above description disclosedwhat I deem to be practical and efficient embodiments of the presentinvention, it should be well understood that I do not wish to be limitedthereto as there might be changes made in the arrangement, dispositionand form of the parts without departing from the principle of thepresent invention as comprehended within the scope of the appendedclaims.

What I claim is:

1. A television system which comprises in combination, a low powertelevision transmitting station, a high power central transmittingstation including means for receiving television signals from said lowpower transmitting station and means for retransmitting said signals, atleast one television receiving station, electronic control means at saidstations, an independent source of alternating current at said firstmentioned transmitting station for feeding said electronic control meansthereat, an alternating current distribution system adapted to feed theelectronic control means at both said central station and said receivingstation, means at said central station for transmitting electric wavesmodulated at a frequency related to that of said distribution system,and means at said first mentioned transmitting station responsive tosaid electric waves for synchronizing said independent current feedsource to said modulation frequency.

2. A television system which comprises in combination, a, low powertelevision transmitting station, a high power central transmittingstation including means for receiving television signals from said lowpower transmitting station and means for retransmitting said signals, atleast one television receiving station, electronic control means at saidstations, an independent source of alternating current at said firstmentioned transmitting station for feeding said electronic control meansthereat, an alternating current distribution system adapted to feed theelectronic control means at both said central station and said receivingstation, means at said central station for transmitting electric wavesmodulated at the frequency of said distribution system, and means atsaid first mentioned transmitting station responsive to said electricwaves for synchronizing said independent current feed source to thefrequency of said distribution system.

3. A television system which comprises in combination, a portabletelevision transmitting station, a high power central transmittingstation including means for receiving television signals from saidportable transmitting station and means for retransmitting said signals,at least one television receiving station, electronic control means atsaid stations, an independent source of alternating current at saidportable transmitting station for feeding said electronic control meansthereat, an alternating current distribution system adapted to feed theelectronic control means at both said central station and said receivingstation, means at said central station for transmitting electric wavesmodulated at a frequency related to that of said distribution system,and means at said portable transmitting station responsive to saidelectric waves for synchronizing said independent current feed source tosaid modulation freqnency.

4. A television system which comprises in combination, a portabletelevision transmitting station, a high power central transmittingstation including means for receiving television signals from saidportable transmitting station and means for retransmitting said signals,at least one television receiving station, electronic control means atsaid stations, an independent source of alternating current at saidportable transmitting station for feeding said electronic control meansthereat, an alternating current distribution system adapted to feed theelectronic control means at both said central station and said receivingstation, means at said central station for transmitting electric wavesmodulated at the frequency of said distribution system, and means atsaid portable transmitting station responsive to said electric waves forsynchronizing said independent current feed source to the frequency ofsaid distribution system.

HENRI DE FRANCE.

